Dual function strap for resonating elements and ultra high frequency antennas

ABSTRACT

A combined EAS and RFID circuit includes an HF coil antenna, a UHF tuning loop, and an RFID chip coupled to a strap that includes a first coupling area and a second coupling area. The coil ends of the HF coil antenna are configured to capacitively and/or conductively couple to one or both of the first coupling area or second coupling area of the strap. The HF coil antenna can include a gap between turns for non-interfering placement of the UHF tuning loop. The EAS circuit can be deactivating upon application of a field at the resonant frequency of sufficient intensity to cause the breakdown voltage to be exceeded between a coil end and coupling area. The threshold breakdown voltage between a coil end and a coupling area can be reduced by laser ablation treatment of a conductive surface of one or both of the coil end or coupling area.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and the benefit of U.S.Utility patent application Ser. No. 15/858,363 filed Dec. 29, 2017, nowpatented as U.S. Pat. No. 10,679,478, which claims priority to U.S.Provisional Patent Application No. 62/440,131 filed Dec. 29, 2016, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject application teaches embodiments that relate generally tocombined HF and UHF circuits, and specifically to coupling regionsconfigured to support both EAS antenna elements and RFID chips.

BACKGROUND

Electronic Article Surveillance (EAS) systems typically operate in thehigh frequency (HF) range, nominally at 8.2 MHz, while certain RadioFrequency Identification (RFID) systems operate in the ultra highfrequency (UHF) range, nominally at 865 MHz. EAS systems typicallyinclude a HF coil antenna coupled to a capacitive element that forms aresonant circuit configured to return a signal when excited by a nearbyfield at the resonant frequency of the EAS circuit elements. UHF RFIDsystems typically include a UHF antenna and/or tuning loop coupled to anRFID chip that powers the RFID chip when excited by a nearby field atthe resonant frequency of the UHF antenna and internal capacitance ofthe RFID chip. The RFID chip sends a coded return signal when powered.Typically, EAS devices and RFID devices are used for different purposesand are manufactured and sold as separate items.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a first configuration of an RFID strap accordingto an embodiment of the disclosure.

FIG. 1B is a diagram of a first configuration of a combined EAS and RFIDcircuit according to an embodiment of the disclosure.

FIG. 2A is a diagram of a second configuration of an RFID strapaccording to an embodiment of the disclosure.

FIG. 2B is a diagram of a laser ablated capacitive plate configured toreduce the threshold dielectric breakdown voltage according to anembodiment of the disclosure.

FIG. 3A is a diagram of a third configuration of an RFID strap accordingto an embodiment of the disclosure.

FIG. 3B is a diagram of a second configuration of a combined EAS andRFID circuit according to an embodiment of the disclosure.

FIG. 3C is a diagram of a UHF tuning loop of the combined EAS and RFIDcircuit of FIG. 3B according to an embodiment of the disclosure.

FIG. 3D is a diagram of a third configuration of a combined EAS and RFIDcircuit according to an embodiment of the disclosure.

FIG. 4 is a diagram of a fourth configuration of a combined EAS and RFIDcircuit according to an embodiment of the disclosure.

FIG. 4A is a diagram of a first configuration of turns of the coilantenna of the combined EAS and RFID circuit of FIG. 4 according to anembodiment of the disclosure.

FIG. 4B is a diagram of a second configuration of turns of the coilantenna of the combined EAS and RFID circuit of FIG. 4 according to anembodiment of the disclosure.

FIG. 5 is a diagram of a first configuration of a folded EAS and RFIDcircuit according to an embodiment of the disclosure.

FIG. 6 is a diagram of a second configuration of a folded EAS and RFIDcircuit according to an embodiment of the disclosure.

FIG. 7 is a diagram of a fifth configuration of a combined EAS and RFIDcircuit according to an embodiment of the disclosure.

DETAILED DESCRIPTION

The systems and methods disclosed herein are described in detail by wayof examples and with reference to the FIGS. It will be appreciated thatmodifications to disclosed and described examples, arrangements,configurations, components, elements, apparatuses, devices methods,systems, etc. can suitably be made and may be desired for a specificapplication. In this disclosure, any identification of specifictechniques, arrangements, etc. are either related to a specific examplepresented or are merely a general description of such a technique,arrangement, etc. Identifications of specific details or examples arenot intended to be, and should not be, construed as mandatory orlimiting unless specifically designated as such.

The present disclosure illustrates new modalities for straps forcombined EAS and RFID circuits. The systems and methods disclosed hereindescribe various aspects of straps and antenna structures for combinedEAS and RFID circuits.

EAS devices and RFID devices are generally designed for differentfunctions and, therefore, are manufactured separately. For example, EASdevices are generally attached to items and are used to prevent theft ofthose items from stores by requiring deactivation of the EAS device at apoint-of-sale terminal when purchased. RFID devices can be used for manydifferent purposes including, for example, item identification, itemtracking, and inventory. As can be appreciated, items can include bothan EAS device and an RFID device to provide the respective benefits ofboth devices. For example, consumer goods can include both an EAS deviceand an RFID device to allow for theft protection and for inventorymanagement.

Combining the functionality of an EAS device and an RFID device into asingle device can provide several advantages. One advantage is thatcombining an EAS device and an RFID device into a single device reducesmanufacturing and inventory costs required for multiple tags. Anotheradvantage is that combining an EAS device and an RFID device into asingle device reduces the number of devices that must be separatelyattached to each item or the number of customized supply chains applyingdifferent tags to items. This reduces the potential for damage to itemsthat might be caused by numerous attachment points to an item. This alsoreduces the number of attached devices that might need to be removed bythe consumer or merchant, potentially saving time and reducing laborcosts. Yet another advantage of combining an EAS device and an RFIDdevice into a single device is that the radio frequency elements can bepurposefully isolated from one another to avoid interference. Whenseparate EAS devices and RFID devices are in close proximity, it ispossible for the radio frequency elements in one device to interferewith the function of the other device. A single combined device can bedesigned to reduce the likelihood of interference.

Turning to FIG. 1A, a strap structure 100 is illustrated. The strapstructure 100 comprises a first coupling pad 102 and a second couplingpad 104. An RFID chip 108 operating in the ultra high frequency (UHF)spectrum, for example at or near 865 MHz, is connected to the strapstructure 100. The frequency of the RFID chip 108 presently set forth isnot limited to any particular frequency. For instance, an RFID chip 108may operate at 13.56 MHz. In certain configurations, the RFID chip 102can be connected via narrow sections 106 of the strap structure 100. Aninductive element, UHF tuning loop 110, can be configured to provide aresonance with the capacitance of the RFID chip 108 in the UHF frequencyrange. The strap structure 100 can be directly coupled, or conductivelycoupled, to the UHF tuning loop 110.

Referring also to FIG. 1B, a coil antenna 112 is coupled to the strapstructure 100. The coil antenna 112 comprises an inner coil end 114 andan outer coil end 116 that interface with the first coupling pad 102 andsecond coupling pad 104 respectively of the strap structure 100. In afirst configuration, as shown in FIG. 1, the coil antenna 112 can becapacitively coupled to the strap structure 100. In a secondconfiguration, the coil antenna 112 can be conductively coupled to thestrap structure 100. The coil antenna 112, due to its structure, canoperate as a slot or pole type UHF antenna. In certain embodiments, anadditional UHF antenna element 118 can be provided.

The coil antenna 112 can be configured such that a gap 120 is createdbetween turns of the coil antenna 112, allowing the UHF tuning loop 110to be placed between the turns of the coil antenna 112 as illustrated inFIG. 1B. This can advantageously ensure that the metal of the coilantenna 112 does not pass directly under the UHF tuning loop 110 whichcould change the inductance of the UHF tuning loop 110 and couldintroduce unwanted losses, or otherwise interfere with the operation ofthe circuit.

The coil antenna 112 resonates with the total capacitance presented bythe strap structure 100 via the UHF tuning loop 110. The UHF tuning loop110 can present a relatively low inductance on the order of about 20 nHto about 30 nH which is negligible at the desired resonant frequency forthe coil antenna 112. The desired resonant absorption frequency for EASsystems is approximately 8.2 MHz. The UHF tuning loop 110 can thereforeoperate as a structure commonly described as a bridge.

A feature of EAS components is the ability to deactivate the EASfunctionality of the circuit at a point of sale terminal when an item ispurchased by a consumer. Typically this is achieved by exposing thecircuit to a strong field at, or near, the circuit's resonant frequency.This exposure of the circuit at the resonant frequency causes a highcurrent to flow in the conductors and an associated high voltage to bedeveloped across the capacity components.

Referring now to FIG. 2A, an improved strap/bridge circuit 200 isdisclosed. In the improved strap/bridge circuit 200, the overlap betweeneach of the coil ends of the antenna coil and the associated couplingpads can be configured to be different. In the embodiment illustrated inFIG. 2A, the inner coil end 214 of the coil antenna can be configured tobe smaller than the outer coil end 216 of the coil antenna. The firstcoupling pad 202 and second coupling pad 204 can be coupled to the innercoil end 214 and outer coil end 216 respectively via an adhesive thatacts as a dielectric between the coil ends and coupling pads. Thecapacitance associated with the coil ends and coupling pads isproportional to the overlap area and is: 1/C_(total)=1/C₁+1/C₂ where C₁is the capacitance between the inner coil end 214 and the first couplingpad 202, and C₂ is the capacitance between the outer coil end 216 andthe second coupling pad 204.

Although the illustration of FIG. 2A shows changes in dimensions onlyfor the coil ends, in other embodiments the sizes of one or more of thecoil ends and/or one of more of the coupling pads can be configured tobe different as would be understood in the art.

The circuit resonates at a resonant frequency that is determined by theinductance of the antenna coil and tuning coil, and the totalcapacitance determined by the configuration of the coil ends andcoupling pads. When an electromagnetic field is presented to the circuitat or around the resonant frequency, a common current flows through thecapacitors C₁ and C₂. The voltage across each of the capacitors C₁ andC₂ is inversely proportional to the capacitance of each. Therefore, byminimizing C₁ and maximizing C₂ it is possible to develop a highervoltage across C₁ than C₂. In this way, the highest possible voltage fora given field strength is developed across C₁. The dielectric (adhesive)used to couple the coil end to the coupling pad can be formulated toundergo a dielectric breakdown at a threshold breakdown voltage that islower than the voltage presented at C₁ but higher than the voltagepresented at C₂. The breakdown voltage can be selected by changing thedielectric constant, the conductivity, thickness, or other suitableproperty of the dielectic (adhesive) so as to make any resonance of thecircuit undetectable by an EAS gate reader system.

To reduce the voltage at which a capacitor breaks down, one or morepoints of separation can be reduced between capacitor places. This canbe achieved by embossing or otherwise mechanically modifying the metallayers of capacitor plates. Similarly, to reduce the breakdown voltagefor C₁ or C₂, one or more points of separation can be reduced between acoil end and a coupling pad. Referring now to FIG. 2B, a structure 220on the metal surface 222 of a coil end (and/or a coupling pad) can bemade using a laser system. In such embodiments, a laser beam 224, oranother suitable means of causing ablation such as an electron beam,causes metal to evaporate at the impact point 226 of the laser beam 224,that also melts adjacent metal 228 which is forced away and up by thepressure of the evaporating metal at the impact point 226. This createsa sharp edged crater-like structure 230 based on the characteristics ofthe laser beam 224, such as how the laser beam 224 is pulsed, the powerincident at the impact point 226, the wavelength, the metal composition,and other factors. In certain embodiments, multiple points on one ormore metal surfaces 222 can be made to decrease the breakdown voltage.

Referring again the circuits of FIGS. 1A, 1B, and 2A, in embodiments theUHF tuning loop 110, 210 can be configured to change properties when ahigh current flows through the UHF tuning loop 110, 210. In certainembodiments, the UHF tuning loop 110, 210 can include a fuse typestructure that causes the UHF tuning loop 110, 210 to become an opencircuit above a threshold AC current. For example, the UHF tuning loop110, 210 can become an open circuit when the EAS function of the circuitis de-activated. By opening the UHF tuning loop 110, 210, the tuning ofthe entire circuit can be changed, leading to a changed read range. Forexample, in certain embodiments, the read range can be greatly reducedor substantially eliminated. In other certain embodiments, the readrange of the circuit could be increased by opening the UHF tuning loop110, 210.) Example fuse type structures can include, but are not limitedto, polymers with conductive particles and/or structures that normallyhave a low resistance but which under localized heating caused by a highAC current are caused to expand non-reversibly and have a highresistance.

Referring now to FIG. 3A, a dual mode strap 300 is illustrated that isconfigured for both a UHF response and a resonance suitable fortriggering an EAS gate. The dual mode strap 300 includes asymmetriccoupling pads and includes a relatively large coupling pad 302 and arelatively small coupling pad 304 that are coupled to a UHF RFID chip308. Referring also to FIG. 3B, the large coupling pad 302 is configuredto be large enough to support a first coupling area 310 and a secondcoupling area 312. The large coupling pad 302 is configured to functionas a bridge across the coil ends of an antenna coil with a definedcapacitance set by the adhesive properties and the overlaps areas asdescribe above. The small coupling pad 302 is configured to support athird coupling area 314 for coupling to an additional UHF antennaelement 318. The dual mode strap 300 can therefore support both resonantabsorption for EAS functionality and UHF RFID functionality as the UHFRFID chip 308 is coupled to the coil antenna at one end and a UHF RFIDantenna at the other end. In certain configurations, the first couplingarea 310, the second coupling area 312, and/or the third coupling area314 can be a different size than the overlap area; for example thecoupling area can be smaller than the overlap area as illustrated inFIG. 3B.

Referring now also to FIG. 3C, in certain embodiments, the dual modestrap 300 of FIGS. 3A and 3B can include a UHF tuning loop 306. Becauseboth coil ends of the coil antenna of FIG. 3B are coupled to the largecoupling pad 302 (and not the small coupling pad 304), the UHF tuningloop 306 can be positioned as shown in FIG. 3C so as to be offset fromthe coil antenna to avoid interference. As described above, the UHFtuning loop 306 can include a fuse type structure that causes the UHFtuning loop 306 to open circuit above a threshold AC current, forexample when the EAS function of the circuit is de-activated.

Referring now also to FIG. 3(d), in certain embodiments, the firstcoupling point 310 and second coupling point 312 can be configured to beasymmetric in size so as to concentrate voltage at one of the couplingpoints (e.g., second coupling point 312, as shown in FIG. 3(d)) forde-activating the circuit by exposing the circuit to a high strengthfield at the resonant frequency of the circuit.

Referring now to FIG. 4, a modified coil antenna structure 400 isdepicted. The modified coil antenna structure 400 is configured to havea large coil with a narrow gap width 402 between turns. This causes thecoil antenna to act a sloop type antenna such that at UHF frequencies,the energy couples across the narrow gap width 402 to form a short atUHF frequencies, but which allows energy at HF frequencies to flowaround the coil antenna turns normally. The coil antenna can include awider gap width 404 for a portion of the coil antenna for UHFfrequencies. A strap 406, tuning loop 408, and RFID chip 410 areincluded as described previously for other embodiments. The couplingbetween the turns can be enhanced by decreasing the gap width by, forexample, laser cutting a narrow gap 420 as illustrated in FIG. 4A,and/or by increasing the relative edge-to-edge area between turns bycutting a curvilinear gap 422 (or cutting any suitable pattern) asillustrated in FIG. 4B.

Referring to FIG. 5, a first embodiment of a foldover circuit 500 ispresented. The foldover circuit 500 can be configured such that when thefoldover circuit 500 is folded at a fold line 502, coupling pad 508 ofthe strap 510 functions as a bridge for coil antenna 512. Coupling pad508 can be conductively coupled to a first coil end 504 of coil antenna512. When foldover circuit 500 is folded, coupling pad 508 can becapacitively coupled to second coil end 506 of coil antenna 512, forexample using a dielectric adhesive as described above. Similarly, anadditional UHF antenna element 518 can be capacitively coupled to thestrap 510 when the foldover circuit 500 is folded.

Referring to FIG. 6, a second embodiment of a foldover circuit 600 ispresented. Foldover circuit 600 can be configured such that when thefoldover circuit 600 is folded at fold line 602, a bridge portion 608(first coupling pad) of the strap 610 contacts a first coil end 606 anda second coil end 604 of coil antenna 612. The bridge portion 608 andcoil ends 606, 604 are capacitively coupled using a dielectric adhesiveas described above. Similarly, an additional UHF antenna element 618 canbe capacitively coupled to a UHF portion 616 (second coupling pad) ofthe strap 610 when the foldover circuit 600 is folded. The strap 610 andRFID chip 614 can be configured on one side of a substrate 620, whilethe coil antenna 612 and UHF antenna element 618 can be configured on asecond side of the substrate 620. The substrate 620 can comprise anysuitable material including, but not limited to, a paper, a card, aplastic such as PET, or a fabric such as nylon or polypropylene. Thesubstrate 620 can be folded at fold line 602 and the two sides laminatedtogether.

Referring now to FIG. 7, in an embodiment a portion of a UHF antenna 718functions as a bridge. In such embodiments, a structure at the end of aUHF antenna 718 commonly described as a top load 720, and comprising arelatively large area of conductor, functions as the resonatingcapacitor in the circuit with the coil antenna 712. To manufacture, theUHF antenna 718 can be applied to the coil antenna 712 or the coilantenna 712 can be applied to the top load 720 portion of the UHFantenna 718. The RFID chip can be directly attached, commonly describedas a flip chip, or can be built with a strap as described above, and canbe attached before or after the coil antenna 712. Additional detailsabout the manufacture and use of RFID straps are described in U.S. Pat.Nos. 7,158,037 and 7,292,148, each incorporated herein by reference intheir respective entireties.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the spirit andscope of the inventions.

What is claimed is:
 1. A device, comprising: a foldover circuit, foldedat a fold line; a strap comprising a bridge portion that contacts afirst coil end and a second coil end of a coil antenna such that thebridge portion and coil ends are capacitively coupled using a dielectricadhesive; and a UHF antenna element that is coupled to a UHF portion ofthe strap when the foldover circuit is folded; and a substrate, whereinthe strap and an RFID chip are configured on one side of the substrateand the coil antenna and UHF antenna element are configured on a secondside of the substrate.
 2. The device of claim 1, wherein the devicecomprises a direct attach chip.
 3. The device of claim 1, wherein thesubstrate is folded at the fold line and the two sides laminatedtogether.
 4. A device, comprising: a Radio Frequency Identification(RFID) chip; an ultra high frequency (UHF) tuning loop conductivelycoupled to the RFID chip; a first coupling pad conductively coupled tothe RFID chip and the UHF tuning loop; a second coupling padconductively coupled to the RFID chip and the UHF tuning loop; and ahigh frequency (HF) coil antenna including a first coil end configuredto couple with the first coupling pad and a second coil end configuredto couple with the second coupling pad; wherein a portion of the UHFtuning loop functions as a bridge such that a structure at the end ofthe UHF tuning loop comprises a large area of conductor and functions asthe resonating capacitor in the circuit with the HF coil antenna.